This invention relates to a power transmission chain. More specifically, it relates to a power transmission chain comprised of a plurality of link plates which are connected by pins and rocker joints.
A silent chain used as power transmission chain for automobiles or motorcycles consists, generally, of a plurality of interleaved links or link-plates. Each link plate has a pair of teeth and a pair of apertures which are connected by pins and rockers, or rocker joints. Each rocker joint includes a pair of long and short pins which are inserted into the pinholes, and rock against one another.
A conventional silent chain is illustrated in FIG. 12. The chain has a construction in which a large number of link plates 50, each having a pair of teeth 51 and apertures or pinholes 52, are connected by rocker joints 60, each of which is composed of a pair of rocker pins 61 inserted in pinhole 52. The configuration of pinhole 52 and rocker pin 61 is shown more clearly in FIG. 13, where flank part 61a of rocker pin 61 contacts pinhole 52 and clearance t' is formed between concave arc surface 61b of rocker pin 61 and pinhole 52.
In the manufacture of silent chain, a preload or tensile load is typically applied after assembly of the chain. The preload causes an alteration of the chain length and provides an initial stress. However, preloading of the chain can also cause cracks or local deformations to occur in the rocker pins on account of the excessive surface pressure generated on the surface of the rocker pins.
In order to prevent the generation of such cracks or local deformations, the surface pressure in the rocker pins is reduced during preloading by increasing the radius of curvature of the rocker pin as much as possible. Such an increase causes wear of the rocker pins and the pinholes when the radius of curvature of the rocker pin is too large.
Usually, a preload (tensile load) is applied to the silent chain after chain assembly for adjustment of the chain length. When the preload is applied to a conventional silent chain, such as shown in FIG. 12, load P' acts on rocker pin 61, as shown in FIG. 13. The flank 61a of the rocker pin 61 presses against the aperture 52 and the aperture 52 is expanded and rocker pin 61 moves to the position shown by the broken line in FIG. 13. As a result, the chain pitch is offset by .DELTA.P with regard to pinhole 52. Therefore, an accurate setting of the chain pitch is not easily attained for the conventional silent chain.
Also, in the conventional silent chain, the dimensions of rocker pin 61 and pinhole 52 are controlled by the distance between flank parts 61a and 61a of rocker pin 61 and the clearances between the aperture wall surfaces and the flank parts 61a. However, the measurement of these dimensions is very difficult, so that dimension control is not easily maintained.
Additionally, in the conventional silent chain, as shown in FIG. 14, the displacement .delta. of the rocker pin in the flank direction (arrow A) is smaller than the displacement .DELTA. in the chain pitch direction (arrow B), when rocker pin 61 is displaced by action of the preload, which is shown by the broken line in FIG. 14. Therefore, the accuracy of setting of the preload needs to be improved in order to obtain accurate adjustment of the chain pitch.